Optical sensing techniques are widely used in automation and other applications. For example, optical sensors are used for detection of movement, presence and absence, and position, of objects in industrial automation process. An example of optical sensors known for such applications is the PX series photo-sensors by Keyence Corporation of the USA.
In a typical optical sensing arrangement, an optical source is arranged on one side of an object for projecting an optical beam towards a destination. An optical detector is positioned on the other side of the object to monitor the detection or reception of optical signals originated from the optical source which are not blocked or intercepted by the objects. Spatial information of the objects, e.g., information on movement, presence and absence, and location, can be obtained from the received optical information. However, such an optical arrangement is known to be bulky and requires expensive components. Further, the reliability of conventional optical sensing arrangements is vulnerable to interference by ambient light noise such as interference from fluorescent lamp and background light. Therefore, it-will be beneficial if there can be provided methods and apparatus of optical sensing to alleviate shortcomings of conventional optical sensing arrangements.